Flue gases, for example, from oil and coal-fired power generation facilities, typically contain corrosive components. The ductwork for carrying such gases in large power generation facilities can be 50 meters above ground level, so that repair and replacement is difficult and costly.
A wide variety of techniques have previously been proposed for the construction or protection of such flue ducts. For example, in low temperature applications, coatings such as vinyl esters or epoxies have been tested. Calendared rubber sheeting has also been considered for protection of the inner duct surfaces. However, this requires either an adhesive or a large number of mechanical fastenings to keep it in place, and has not provided a satisfactory means of protection.
Ducts have also been constructed of corrosion-resistant metals. Galvanized steel offers some protection against corrosive gases, while chromium-nickel alloys such as Hastalloy provide more effective protection. However, the high cost and difficulty in fabrication make such alloys an unattractive alternative. Still other protective measures that have been explored include the use of fluoroelastomer-based coatings. However, the solvents used in such coatings are difficult to handle, the coatings can only be applied in thin layers, and extensive preparation of the surface to be coated is generally necessary.